1. Field of the Invention
The present invention relates to a wire electric-discharge machine for machining a workpiece by supplying electricity to a wire electrode.
2. Description of the Related Art
FIG. 1 is a diagram schematically illustrating a wire electric-discharge machine.
In the drawing, reference numeral 1 denotes a bed, i.e., a base of the machine, on which an X-Y axis driving unit is mounted. Numeral 2 denotes an X-axis table which is movably supported by means of an X-axis slide 4 which, in turn, is movably supported by an X-axis guide 3 fixed to the bed 1. Numeral 5 denotes an X-axis ball screw; 6, a table for fixing a workpiece; 7, a processing tank for storing a working fluid; and 8, a column for supporting a Z-axis unit 9, a lower arm 10a being fixed to the column 8. Further, the column 8 is either fixed or movable along the direction of the longitudinal axis of the lower arm 10a. A lower guide 11a is attached to a distal end of the lower arm 10a, and effects a change in the direction of a wire electrode 12 by means of a roller provided therein.
Numeral 13a denotes an upper guide fixed to a distal end of the Z-axis unit 9. Numeral 14 denotes a Y-axis guide which is fixed to the top of the bed 1, and a Y-axis slide 15 is engaged therewith and is supported in such a manner as to be movable in the axial direction. Numeral 16 denotes a Y-axis ball screw, and 17 and 18 denote Y-axis and X-axis motors, respectively. Numeral 19 denotes a wire recovering device which supports a recovery roller 20 for recovering the wire electrode 12 and is fixed to the column 8. Numeral 21 denotes a recovery box for accommodating the recovered wire electrode 11. Numeral 22 denotes a wire bobbin; 23, a pad disposed underneath the bed; and 24, a leveling bolt for adjusting the inclination of the overall machine. Next, a detailed description will be given of the lower guide 11a.
FIGS. 15 and 16 are diagrams illustrating the conventional lower guide in the wire electric-discharge machine shown in FIG. 1. FIG. 15 is a horizontal sectional view of a portion of the lower guide 11a, and FIG. 16 is a longitudinal sectional view taken along the axial direction of the lower guide 11a.
The lower guide 11a is fixed to a distal end of the lower arm 10a by means of bolts 202 via an insulating plate 201. This attaching surface is perpendicular to the distal end of the lower arm 10a. The lower guide 11a is mainly comprised of a lower nozzle 203, an electrical supply die 204, a lower wire guide holder 205, a guide supporting plate 206, and a lower block 207, and the fixing of the lower guide 11a to the lower arm 10a is mainly effected by the lower block 207.
The lower wire guide holder 205 has an elongated hollow cylindrical shape, is provided with a wire guide 205a at its upper distal end for precisely guiding the wire electrode, and is screwed into and fixed in the lower block 207. The lower block 207 includes a roller 208, and a change in the direction of the wire electrode 12 is effected by a wire passage 207c. The wire passage 207c has a tapered wire inlet 207a and a tapered wire outlet 207b. A recovery pipe 209 is connected to the outlet 207b. Further, a lower transport-stream outlet 210 is provided to allow a transport stream to spout for transporting to the wire recovering device 19 the wire electrode 12 whose direction has been changed by the roller 208.
The guide supporting plate 206 incorporates the electrical supply die 204. The electrical supply die 204 is fixed between the guide supporting plate 206 and an electrical-supply-die holding plate 211. In addition, the guide supporting plate 206 incorporates a drawing-out board 212 for drawing out the electrical supply die 204. Numeral 213 denotes a lower auxiliary guide which is structured so as to press the wire electrode 12 against the electrical supply die 204 in cooperation with the lower wire guide holder 205.
The lower nozzle 203 is a portion for jetting a working fluid, and a working fluid is supplied to its interior as a high-pressure fluid through a pipe 214. Numeral 215 denotes a spring, and 216 denotes a pressing plate of the lower nozzle 203. During machining, the lower nozzle 203 is raised by means of the working fluid supplied to its interior while compressing the spring 215, and is stopped by the pressing plate 216, and during nonmachining, the lower nozzle 203 returns downward since the working fluid is not supplied. In addition, the lower nozzle 203 has such a configuration that the cross-sectional area of its upper surface decreases gradually toward its distal end so as not to come into contact with the lower wire guide holder 205 when the working fluid ceases to be supplied and the lower nozzle 203 returns downward.
Reference numeral 217 denotes the wiring which is connected to the supporting plate 206 so as to supply a working electric current from a power supply to the electrical supply die 204. Naturally, the guide supporting plate 206 is formed of an electrically conductive material. Reference numeral 218 denotes a bolt which serves to fix the guide supporting plate 206 onto the lower block 207. A passage 219 is provided in a distal end portion of the lower wire guide holder 205 in the vicinity of the wire guide 205a. This passage 219 is used to allow the working fluid to flow for cooling the heat which is generated due to electrical discharge through contact energization between the electrical supply die 204 and the wire electrode 12 as well as Joule heat which is generated as electric current flows across the wire electrode 12. This passage 219 is formed by branching a portion of the pipe 214 to supply the working fluid without causing a decline in the internal pressure of the lower nozzle 203. Further, the working fluid for cooling passes through the lower auxiliary guide 213 and the recovery pipe 209, flows in the downstream direction, and is recovered.
Reference numeral 220 denotes a terminal to which the wiring 217 is connected and which is disposed on a side surface of the guide supporting plate 206. Numeral 221 denotes a pipe end, to which the pipe 214 is connected and which is disposed on a side surface of the guide supporting plate 206. Numeral 222 denotes a rectifying plate which is located inside the lower nozzle 203 to rectify the flow of the working fluid sent front the pipe end 221 to the interior of the lower nozzle 203. Numeral 223 denotes a bolt.
Further, a detailed description will be given of the upper guide 13a.
FIG. 17 is a longitudinal sectional view taken along the axial direction of the upper guide 13a shown in FIG. 1.
The upper guide 13a is fixed to a distal end of the Z-axis unit 9 by means of an attaching plate 250. Numeral 251 denotes an upper block to which are attached an electrical supply die 252, an upper wire guide holder 253, a housing 254, a jet nozzle 255, and upper nozzle 256. The upper wire guide holder 253 has an elongated hollow cylindrical shape, is provided with a wire guide 253a at its lower distal end for precisely guiding the wire electrode, and is screwed into and fixed in the upper block 251.
The jet nozzle 255 is used to insert the wire electrode 12 by guiding the same by means of a water jet, and is accommodated in the space between the housing 254 and the upper wire guide holder 253 by means of a spring 257 in such a manner as to be movable in the vertical direction.
Reference numeral 258 denotes a working fluid passage for supplying a pressurized working fluid. This working fluid supplied to the upper guide 13a first enters a space 254a surrounded by the housing 254 and the upper nozzle 256, then passes through a working fluid passage 254b in the housing 254, is further sent to a space 254c surrounded by the housing 254 and a tip portion of the upper nozzle 256, and is jetted out from a jetting port 256a provided in the tip of the upper nozzle 256. Incidentally, such a method of transporting a working fluid is also described in Japanese Patent Application Laid-Open No. 121421/1982. In addition, in the upper wire guide holder 253 as well, a passage 259 is provided in the vicinity of an upper portion of the wire guide 253a in the same way as in the lower wire guide holder 205. This passage 259 is used to take in the working fluid by making use of the internal static pressure within the upper nozzle 256 during machining, and is used for cooling the wire electrode 12 inside the upper wire guide holder 253 and for cooling a contact energization portion of the electrical supply die 252.
Reference numeral 260 denotes a jet pipe which is passed through the attaching plate 250 and the upper block 251, and leads to the portion of the upper wire guide holder 253 which is attached to the upper block 251. The working fluid flows in the interior of the jet pipe 260, and the arrangement provided is such that, after being temporarily accumulated in the internal space of the jet nozzle 255, the working fluid spouts from the tip of the jet nozzle 255 in the form of a jet stream of a small diameter so as to supply the wire electrode 12 to the lower guide 11a. Numeral 261 denotes an upper auxiliary guide; 262, an electrical-supply-die pressing plate for the electrical supply die 252; and 263, a drawing-out board.
As described above, in the lower guide 11a of the conventional wire electric-discharge machine, the wire electrode is sent from the upper guide 13a to the lower guide 11a, the working electric current is supplied to the wire electrode 12 by the electrical supply die 204 and is transmitted to a workpiece so as to be used in machining. In this case, in portions of contact between the electrical supply die 204 and the wire electrode 12, heat is generated due to a very small amount of electrical discharge, and Joule heat is also generated as the electric current flows across the wire electrode 12. Therefore, the working fluid is allowed to flow along the wire electrode 12 to effect cooling by making use of the internal static pressure of the nozzle 203 through the passage 219 so as to prevent the wire electrode 12 from becoming cut off by this heat. However, since there is a distance between the electrical supply die 204 and the workpiece, the working electric current is limited owing to the resistance of the wire electrode 12 itself and an increase in resistance due to a temperature rise, so that there has been a problem in that the machining efficiency declines.
It should be noted that, in the conventional configuration, the lower wire guide holder 205 has a hollow cylindrical shape as illustrated, and the electrical supply die 204 is disposed below the lower wire guide holder 205, so that it is extremely difficult to locate the electrical supply die 204 close to the tip of the lower nozzle 203. A similar problem occurs with the upper guide 13a as well.
The electrical supply die 204 presses the wire electrode 12 against the guide supporting plate 206 by means of the electrical-supply-die holding plate 211 to provide reliable contact with the guide supporting plate 206, and contact-supplies to the wire electrode 12 the working electric current supplied from the wiring 217. In this case, if machining is effected by supplying electric power for a fixed time duration, the electrical supply die 204 becomes worn due to the effect of the very small amount of electrical discharge, so that it is necessary to periodically replace the electrical supply surface of the electrical supply die 204 which comes into contact with the wire electrode 12. In this replacement, it is necessary to remove the electrical-supply-die holding plate 211, draw out the electrical supply die 204 to the outside by means of the drawing-out board 212, index a new position for the electrical supply die 204, and then fix the electrical supply die 204 in the reverse order. Hence, there has been a problem in that this operation is troublesome, and that the machine must be stopped at the same time. A similar problem occurred with the upper guide 13a as well.
Further, if the diameter of the wire electrode 12 is different, the wire guide 253a of the upper wire guide holder 253 needs to be replaced with one which matches the same. As for the jet nozzle 255 as well, the selection of a jet nozzle optimally suited to the diameter of an insertion hole provided in the workpiece is important in enhancing the reliability of insertion. At the time of replacement of the wire guide 253a and the jet nozzle 255, it is necessary to remove the upper nozzle 256, the housing 254, and the jet nozzle 255, and subsequently remove the upper wire guide holder 253 from the upper block 251 by means of a tool or the like. During reinstallation, it is necessary to effect operation in the reverse order. Hence, there has been a problem in that disassembly and reinstallation have been time-consuming and troublesome.
Further, in the lower guide 11a, the working fluid is allowed to flow along the wire electrode 12 through the passage 219 from the interior of the lower nozzle 203 by making use of the back pressure so as to cool the wire electrode 12. However, because of the prevention of interference of the workpiece and the lower nozzle 203 with a jig or the like and because of steps in their configurations, there is a case where the workpiece and the lower nozzle 203 are disposed in spaced-apart relation to each other to effect machining, so that there has been a problem in that sufficient back pressure cannot be obtained, resulting in a shortage in a flow rate for cooling. Further, although it is possible to enlarge the passage 219 for solving this problem, the flow rate for cooling becomes too high in the case of contact machining in which the lower nozzle 203 is held in contact with the workpiece. As a result, secondary trouble such as the vibration of the wire electrode 12 can occur, or it becomes necessary to replace the guide with one in which the diameter of the passage 219 is different in correspondence with the machining state. Hence, the enlarging of the passage 219 is very inconvenient. A similar problem occurs with the upper guide as well.
In addition, in general, the passage 219 for cooling is frequently formed with a small diameter of 1 mm or less. However, if the lower wire guide holder 205 is magnetized due to the effect of the magnetic field where the working electric current flows, machining sludge and metal powder contained in the working fluid are deposited, and if the machine is used over extended periods of time, clogging can occur, and the flow rate for cooling becomes insufficient. Hence, there has been a problem in that periodic cleaning must be provided to overcome this problem. In particular, clogging is liable to occur during non-contact machining in which back pressure is difficult to operate. Incidentally, it is estimated that the action of a local cell occurring in the conductor in water also functions in this phenomenon, and it is difficult to overcome this phenomenon.
The wire electrode 12 which is passed through the lower guide 11a and is inserted has its direction changed by the roller 208 toward the wire recovering device 14, and is transported by the lower transport stream. However, as shown in FIG. 16, the lower transport-stream outlet 210 is provided on the same line as the recovery pipe 209, so that after the wire electrode passes through the lower auxiliary guide 213, the transport of the wire up to the roller 208 is left to the linearity based on the rigidity of the wire electrode 12 itself. Accordingly, there are cases where the wire electrode becomes buckled midway, so that there has been a problem in that trouble due to buckling or the like is unavoidable by the use of the wire inlet 207a alone.
In addition, the lower nozzle 203 of the lower guide 11a has such a configuration that its cross-sectional area decreases gradually toward its distal end, and the stream of the working fluid after passing through the rectifying plate 222 is temporarily accumulated in the inner space of the lower nozzle 203. Subsequently, the working fluid is jetted out from the jetting port, but since the working fluid is jetted out without conversion of dynamic pressure to static pressure, the velocity component of the stream does not become uniform at the jetting port and forms turbulence. Hence the working fluid jets out without its direction being fixed. For this reason, machining becomes incomplete, and if the flow rate of the working fluid is low, the stream becomes biased, so that there has been a problem that a large influence is exerted on the machining capability.
In particular, under the machining condition in which the working fluid needs to flow at a very small flow rate and a small working electric current is applied, or in a case where the diameter of the wire electrode 12 is made small, the turbulence of the working jet exerts a very large influence on the performance. Hence, a jet-having a uniform flow rate is required, and the volume of the internal space of the lower nozzle 203 alone does not produce sufficient conversion to static pressure. Further, to obtain sufficient static pressure for the working fluid inside the lower nozzle 203, it is necessary to supply the working fluid to the interior of the lower nozzle 203 uniformly in a state in which the flow rate is reduced, and it is difficult to realize this state by the use of the few jetting ports conventionally provided.
Although the wire electrode 12 supplied from the upper guide 13a by means of the jet stream is guided to the lower guide 11a through the tapered guide provided at the distal end of the lower guide 11a, the jet stream does not necessarily advance straightly downward due to the shape of the workpiece or the shape of the wire passing hole. Hence, in a case where the jet stream has become biased, there has been a problem in that the wire electrode 12 fails to be inserted into the lower guide 11a, resulting in the shutdown of the machine or imposing restraints on the working profile.
It should be noted that a wire electric-discharge machine disclosed in Japanese Patent Application Laid-Open No. 104618/1985 is also known as a conventional example. In this wire electric-discharge machine as well, the wire holder has an elongated hollow cylindrical shape, and a substantial distance is present between the electrical supply die and the tip of the nozzle, and the problem that the working electric current is restricted is not solved.
In addition, a wire electric-discharge machine disclosed in Japanese Patent Application Laid-Open No. 30919/1992 is also known as a conventional example. The lower guide of this wire electric-discharge machine is structured such that the portion corresponding to the lower wire guide holder has not a hollow cylindrical shape but the shape of a rectangular parallelopiped, and the electrical supply die is provided therebelow. However, a substantial distance is present between the electrical supply die and the tip of the nozzle, and the problem that the working electric current is restricted is not solved.
In addition, as a conventional example there is known an electrical supply tip of a wire electric-discharge machine having a plurality of grooves as disclosed in Japanese Utility Model Application Laid-Open No. 89433/1986. Even if this electrical supply die is used, it is impossible to solve the problem that when the electrical supply tip has become worn due to the contact electric discharge, after removing the electrical supply tip and indexing a new position, it is necessary to fix the electrical supply tip in the reverse order, which requires time and trouble.
Furthermore, a wire electric-discharge machine disclosed in Japanese Utility Model Application Laid-Open No. 116126/1984 is also known as a conventional example. The shape of the lower nozzle of this wire electric-discharge machine is arranged such that its cross-sectional area decreases gradually toward its distal end. Even if a partition plate is provided, the problem that the velocity component of the stream does not become uniform at the jetting port and forms turbulence and the working fluid jets out without its direction being fixed is not sufficiently solved.